This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations and terms are herewith defined:
ACK/NACK acknowledgement/negative acknowledgement
BER/BLER bit error rate/block error rate
CQI channel quality information
DL downlink
DTX discontinuous transmission (e.g., CQI-only transmission)
E-UTRAN evolved UTRAN
3GPP third generation partnership project
LTE long term evolution of 3GPP
Node B base station or similar network access node
OFDM orthogonal frequency division multiplex
PUCCH physical uplink control channel
SER symbol error rate
UE user equipment (e.g., mobile equipment/station)
UL uplink
UMTS universal mobile telecommunications system
UTRAN UMTS terrestrial radio access network
3GPP is standardizing the long-term evolution (LTE) of the radio-access technology which aims to achieve reduced latency, higher user data rates, improved system capacity and coverage, and reduced cost for the operator. A significant distinction in LTE over prior generation wireless systems is that the base station, termed in LTE as an e-Node B, has much broader latitude in scheduling radio resources in use in its cell, and need coordinate with higher network nodes to a much lesser extent than in older systems. This reduces latency in that the e-Node B can make snap decisions for its own resource allocations. More efficient use of the available resources can be achieved with more information at the e-Node B on which to base those allocation decisions. There is of course a point of diminishing returns wherein additional information reported back to the e-Node B by the mobile stations occupies more bandwidth and resources as control signaling than are saved by the more efficient allocation.
Some of that control signaling is a channel quality indicator CQI that tells conditions of the channel over which a transmission to the mobile station was received, and also acknowledgements (ACK) and negative acknowledgements (NACK) that tell whether the mobile station received and properly decoded control signaling or data that was intended for it. In LTE, these feedbacks are sent by the mobile stations on what is termed the physical uplink control channel PUCCH.
While LTE is not yet finalized, it is currently understood among various groups working to finalize its details that the mobile station is to send is CQI bits and its AKC or NACK bit(s) simultaneously in response to reception on a downlink DL. This enables the e-Node B to perform more accurate forward error correction on the channel over which that DL was sent, the next time the e-Node B uses that same channel, or others in which it might be closely related. It is noted that in LTE at least, ACK/NACK requires a smaller BER than CQI does, and that the ACK/NACK transmission and the CQI-only transmissions have to be separated. CQI may sometimes be sent with uplink data but for the case where it is not (e.g., where the mobile station does not have data in its buffer to transmit or it is not granted uplink resources for data transmissions) it is sent without any accompanying data. These ACK/NACK/CQI-only signals are referred generally as data non-associated control signalling since the mobile station sends them without accompanying user data. The principle of simultaneous transmission of different data non-associated control signalling may also be applicable to other systems; LTE is used only as an example.
A problem arises in that generally there are a number of bits needed for reporting CQI, and only one or two bits are needed for reporting ACK or NACK (in LTE, one bit ACK./NACK is used for BPSK modulation and 2 bits for QPSK modulation). Two solutions are proposed of which the inventor is aware, commented below.
A first proposed solution is that the LTE standard require joint coding of CQI and ACK/NACK. At least two problems are seen in this approach: the ACK/NACK bit error rate BER may be too high if there is no repetition before encoding; and that there is no way to distinguish a transmission having CQI sent with ACK/NACK from a transmission with CQI sent alone.
DTX/ACKNACK modulates a reference sequence (RS) and if ACK/NACK is present, a number of symbols are allocated to ACK/NACK. With this proposed solution, if detection of the DTX/ACKNACK is in error then the CQI decoding is not likely to be successful. Also, performance degrades in the presence of ACK/NACK bit(s) and the applicability of a two-bit ACK/NACK is limited to QPSK modulation and is not seen to carry any further information when BPSK modulation is used. Further, the invention detailed below gives improved performance.
What is needed in the art is a way to simultaneously signal different types of data non-associated control signaling with acceptable performance and without increasing control signaling overhead to a detrimental level.